Downflow air filter construction and methods for air flow adjustment and leak testing thereof

ABSTRACT

A HEPA-type, downflow air filter module is disclosed, having a damper supported upon a hollow tube for adjustable movement relative to an opening through which air enters the enclosed chamber or plenum above the filter media. The hollow damper support tube is axially aligned with a passageway between upstream and downstream sides of the center board which conventionally separates the media core into two halves in such filter modules. The passageway is normally sealed by a plug which may be removed from the downstream side of the module for measuring and adjusting air flow into the module, as controlled by the position of the damper which may be adjusted while air flow is being measured. The filter construction also permits leak testing of the filter by injection of test smoke from the downstream side, through the center board passageway and hollow damper tube, with simultaneous monitoring of the smoke concentration on the upstream side, thereby insuring that the desired level of smoke concentration on the upstream side of the media is reached prior to scanning the downstream side for the presence of particles to detect leaks.

BACKGROUND OF THE INVENTION

The present invention relates to novel constructions of air filter unitsof the downflow, HEPA type, and to methods of measuring and adjustingair flow into such filter constructions and of performing leak testingthereof.

In locations requiring air substantially free of all foreign matter,such as for industrial process or medical applications, it is a commonpractice to provide high efficiency filter modules having media corescapable of removing essentially all particles down to sub-micron sizethrough which all entering air passes. The media is sealed about itsperiphery to housing structure including a center board dividing themedia core into two halves and defining an enclosed chamber or plenum onthe upstream side of the media.

Incoming air is directed by a fan through suitable ductwork to theindividual filter modules which are suitably supported and sealed tosurrounding structure with the downstream face of the filter mediaforming a portion of the ceiling of the room to which the filtered airis supplied. Air from the ductwork enters the enclosed space on theupstream side of the media through an opening in the top wall of thehousing structure. The rate of air flow into the filter plenum iscontrolled by the position of a damper mounted for adjustable movementwith respect to the opening through which air enters from the ductwork.

It is desireable to test such filter modules periodically afterinstallation for leaks in order to verify that the required level offiltration efficiency is being maintained. This has been done in thepast by developing standard test fluids, such as D.O.P. smoke, which areplaced in suitable concentrations on the upstream side of the filtercore while scanning the downstream side with sensing equipment to detectthe presence of particles which have leaked through or around the media.Although such functions as damper adjustment, air pressure measurement,and test smoke injection and upstream concentration monitoring may beperformed from the upstream side of the media, they normally may be moreconveniently carried out from the downstream side, assuming suitableprovision is made in the filter module construction.

In U.S. Pat. No. 3,522,724, three passageways are formed through thecenter board of the filter housing, each providing communication betweenthe upstream and downstream sides of the media. The slotted lower end ofan elongated rod may be engaged by a screwdriver inserted through thecenter opening, rotation of the rod serving to adjust the position ofthe damper, thereby changing the rate of air flow into the filterplenum. For leak testing, test smoke is injected directly into thefilter plenum through one of the other openings while the concentrationof the smoke on the upstream side of the media is monitored through thethird opening. Thus, in order to adjust the position of the damper,inject test smoke into the filter plenum, and monitor the concentrationof the smoke within the plenum, three separate and distinct passagewaysthrough the media, or, more commonly, the center board dividing themedia into two halves, have heretofore been employed.

Each of the three openings is sealed, of course, when not in use for theintended purpose by a plug removable from the downstream side of thefilter unit. However, the more openings or passageways which areprovided between upstream and downstream sides of the media, the greaterthe possibility of leaks occurring when the filter is in use and suchpassageways are presumably sealed. While injecting the test smokedirectly into the filter plenum from the downstream side has theadvantage of confining the smoke to a single plenum, it is difficult todistribute such smoke evenly over the upstream side; consequently, theconcentration of smoke monitored through an opening at a discrete pointabove the filter media may not accurately reflect the concentration ofsmoke over the entire upstream face. Furthermore, while adjustment ofthe damper position from the downstream side of the filter unit tocontrol the rate of air flow from the ductwork into the plenum isconvenient, no means have been provided in such filter units for takingmeasurements from the downstream side indicating the actual rate of airflow at any given time.

The principal object of the present invention is to provide a downflow,HEPA-type air filter construction which is both simpler in constructionand more versatile in operation, adjustment and testing than prior artconstructions of this type.

Another object is to provide a HEPA-type air filter module havingfeatures facilitating the direct measurement of air pressure readings,from the downstream side of the media, in the ductwork directly abovethe module.

A further object is to provide a downflow air filter having a plenumchamber on the upstream side of a media core and an adjustable dampercontrolling the rate of air flow from ductwork into the plenum whereinthe damper may be adjusted simultaneously with direct measurement of theair flow rate controlled thereby.

Still another object is to provide a HEPA-type air filter havingimproved leak testing features; more specifically, this object is toprovide means for injecting test smoke from the downstream to theupstream side of the media which assures uniform distribution of thesmoke over the upstream face.

A still further object is to provide a HEPA-type air filter constructionhaving a single passageway through the media center board through whicha wand may be inserted for injection of test smoke from downstream toupstream sides of the filter media while simultaneously monitoring theconcentration of such smoke on the upstream side through the samepassageway.

Another object is to provide novel and improved methods of effectingdamper adjustment, making air pressure and flow measurement, injectingtest smoke and monitoring the upstream concentration thereof for leaktesting in downflow, HEPA-type air filter modules.

Other objects will in part be obvious and will in part appearhereinafter.

SUMMARY OF THE INVENTION

The invention comprises an air filter construction having the usualfilter core of pleated media divided by a center board, sealinglymounted in a housing having an enclosed plenum above the media with anupper, centrally disposed air inlet opening and a damper mounted foradjustable movement with respect thereto, with novel features fulfillingthe aforementioned objects. Such novel features include a hollow tubeaxially aligned with a single passageway through the media center boardand operatively connected to the damper to effect adjusting movementthereof in response to rotation of the tube. In the preferredembodiment, the damper is conical in shape, perforated and supporteddirectly upon the hollow tube.

The lower end of the damper support tube is accessible for engagement byan adjusting tool inserted through the passageway, and a pitot tubeprobe connected to air pressure measurement apparatus may be insertedthrough the passageway and damper support tube to make pressuremeasurements in the duct above the module. By making the adjusting toolin the form of a second hollow tube, axially aligned with the dampersupport tube when extending through the passageway with adjoining endportions of the two tubes operatively engaged, the pitot tube may beextended through both tubes and pressure readings taken simultaneouslywith moving the tool to effect adjusting movement of the damper.

The hollow damper support tube may also be used for insertion of ahollow wand, connected to a conventional test smoke generator, forinjecting smoke from the downstream side of the filter into the ductworkabove the damper. The smoke will be carried by the air flowing from theductwork into the filter plenum, over the damper and through theperforations therein, being mixed well with the incoming air anddistributed evenly over the upstream face of the media. Further uniquestructure permits the upstream concentration of the test smoke to bemonitored through the same, single, center board passageway. Leaktesting is then performed in the usual manner by scanning the downstreamface of the media with apparatus adapted to detect the presence of smokeparticles which have passed through the filter.

These and other unique features of the filter construction and themethods of air pressure/flow rate measurement and leak testing madepossible thereby will be more readily understood from the followingdetailed description, taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, elevational view, in section through thecenter, of a filter construction embodying various constructionalfeatures of the invention, and illustrating the preferred method of leaktesting thereof;

FIG. 2 is an exploded perspective view of the filter construction ofFIG. 1;

FIG. 3 is an assembled, perspective view, with portions broken away,thereof;

FIG. 4 is an enlarged, fragmentary, elevational view of a portion of thefilter construction of FIGS. 1-3;

FIG. 5 is a perspective view of an element of the filter construction,including an alternate form of the construction;

FIG. 6 is an elevational view, in section through the center, of thefilter construction incorporating the portion shown in FIG. 5, andillustrating the preferred method of damper adjustment and measurementof air flow controlled thereby;

FIG. 7 is an exploded perspective view of the adjusting tool shown inFIG. 6; and

FIG. 8 is an enlarged, fragmentary, perspective view of an end portionof the tool of FIG. 7.

DETAILED DESCRIPTION

Referring now to the drawings, in FIGS. 1-3 is shown an air filtermodule, denoted generally by reference numeral 10, in FIGS. 1-3. Afilter core is formed in conventional fashion by pleating in accordianor zig-zag fashion first and second sheets of filter media 12 and 14,each continuously sealed along one side to center board 16, which thusdivides the pleased media into two halves. The opposite sides of eachpleat are maintained in spaced relation by corrugated spacers, inaccordance with conventional practise for such filters. The filter coreis enclosed by a box-like housing or hood which may be fabricated in anumber of ways, the illustrated form including side panels 18 and 20,end panels 22 and 24, and top wall 26.

Media sheets 12 and 14 are sealed continuously on all four sides to theside and end panels of the hood. Since end pleat 28 and the pleat at theopposite end provide continuous surfaces, they may be sealed to endpanels 22 and 24 by a continuous bead of a suitable adhesive. The sameapplies to the sealing of media sheets 12 and 14 to center board 16. Thezig-zag edges of the media are preferably completely enclosed is a layerof the adhesive, which may be accomplished by using side panels 18 and20 as shallow pans into which a layer of liquid adhesive is poured. Thecomplete edges of the media are immersed in the adhesive, which thenhardens to form the continuous seal in the general manner described inU.S. Pat. No. 4,227,953.

A layer of insulation 30 is provided in covering relation to the top andend walls of the housing. Centrally disposed openings 32 and 34 areformed in top wall 26 and insulation layer 30, respectively. Cylindricalcollar 36 curves smoothly outward around its lower periphery to flange38, in a plane perpendicular to the central axis of the collar. Whenassembled, collar 36 extends through openings 32 and 34 with flange 38on the lower side of top wall 26, as shown in FIG. 1, and tack weldedthereto. The dimensions and configuration of the housing are such thatan enclosed space or plenum 40 is provided on the upstream side of thefilter core.

Cylindrical duct section 42 is connected to collar 36 as shown in FIG. 1to supply incoming air to plenum 40. In the usual applications, aplurality of filter modules 10 will be suspended by and sealed tosuitable support structure above the room or other space to whichfiltered air is to be supplied, forming all or part of the ceiling, theroom being otherwise sealed against incoming air. The cylindricalductwork sections connected at one end to the filter modules arenormally connected at the other end to a larger duct, forming anincoming air plenum with a blower or fan at the inlet. Perforatedaluminum screen 41 is attached to the housing, in covering relation tothe downstream media face, also in conventional fashion.

Turning now to the unique constructional features of the presentinvention, the rate of air flow from duct 38 into plenum 40 iscontrolled by the position of damper 42, preferably conical in shape andperforated over substantially its entire surface, with respect to theopening in collar 36. Damper 42 is fixedly supported by weld nuts 44upon hollow damper support tube 46 at a position adjacent the upper endthereof. Tube 46 is externally threaded from the lower end for a portionof its length. In the embodiment of FIGS. 1-4, a second hollow tube 48extends at least partially through a passageway between the upstream anddownstream sides of the filter core, through center board 16 and issealed to the upper side thereof by a bead of sealant 50.

Threaded fitting 52 is attached to the upper end of tube 48, withinplenum 40 and the lower end of tube 46 is threaded into fitting 52, tube46 thereby being supported upon tube 48 for axial movement in responseto rotation of tube 44. One or more openings 54 (two of which areillustrated) are formed through the wall of tube 48 within plenum 40.The passageway through center board 16 is sealed by a plug, provided forsuch purpose and removable from the downstream side of the module, asshown, for example, in previously mentioned U.S. Pat. No. 3,522,724,when in operation. Removing the plug provides access to the lower end oftube 44 for rotation thereof by an adjusting tool, to effect movement ofdamper 42 relative to the air inlet opening in a manner explained later.

The construction just described permits leak testing of filter module 10in a novel and unique manner, which will now be described withparticular reference to FIG. 1. HEPA-type filters are commonly testedfor leaks according to prescribed standards by placing a test fluidcarrying at least a prescribed minimum concentration of contaminants onthe upstream side of the media, i.e., within plenum 40 in the presentconstruction, and scanning the downstream side with detection apparatusto indicate the presence of contaminants which have passed through themedia. A common test fluid is that known as D.O.P. smoke, and thepresence or concentration thereof may be detected or registered by aconventional photometer. D.O.P. smoke generators and photometers, bothportable in nature, are commercially available from a variety ofsources.

Thin, hollow wand 56 is connected by tubing 58 to a portable D.O.P.smoke generator (not shown). Wand 56 passes in sealed engagement throughresilient stopper 60 in an opening in the bottom wall of cup 62. Tubing64 passes through an opening in the side of cup 62, being sealedthereto, and is connected by tubing 66 to a portable photometer (notshown). The outside diameter of wand 56 is such that it may be insertedthrough damper support tube 44, and the wand length is such that end 68thereof is positioned above the upper end of damper tube 44, within duct38, when fully inserted as shown in FIG. 1 with resilient lip 70 of cup62 in sealing engagement with the module about the opening at the lowerend of the passageway through center board 16.

With the leak testing equipment so positioned, the smoke generator isturned on and smoke is injected from end 68 of wand 56 above collar 36.Injecting the smoke into this area where the velocity of air moving fromduct 38 into plenum 40 is high, and passing the smoke over and throughdamper 42 as it is drawn into the plenum, assures the best possiblemixing and even distribution of the test smoke over the upstream side ofthe media. Plenum 40 communicates, through openings 54, tube 48, cup 62,and tubing 64 and 66 with the photometer, thus permitting measurement ofthe concentration of test smoke on the upstream side of the mediathrough the same, single, center board passageway used for injection ofthe smoke. Although the clearance between the outside and inside oftubes 46 and 48, respectively, may be small, it is sufficient even ifthe only path for the smoke is through the threads on the outside oftube 46.

With smoke being thus introduced into plenum 40 and the photometersampling upstream concentration through cup 62, the photometer isadjusted for 100% per manufacturer's instructions. The smoke generatoris then turned off, wand 56 is removed from cup 62 and reinsertedthrough tubes 48 and 46 with stopper 60 sealingly engaged in the openingat the lower end of the passageway through center board 16. Cup 62 isdisconnected from the photometer and the standard sampling probe whichis provided as a component of the photometer is connected thereto. Thesmoke generator is then started again and while test smoke continues tobe injected into the area above the module and carried into plenum 40,the photometer sampling probe is held in close proximity to thedownstream face of the media.

The hand-held probe is moved by the operator across the media face untilthe entire module 10, including the perimeter where the module restsupon the support structure (usually a suspended T-bar grid), has beenscanned. The photometer will register the presence of any particles fromthe test smoke which have leaked through or around the media. If anyleaks are found which are larger than the rated efficiency of thefilter, they are sealed with an appropriate sealant such as RTVsilicone.

Turning now to the second disclosed construction, wherein the samereference numerals are used to denote elements which are common to thetwo constructions, bar 72 extends across and is fixedly attached to theupper end of collar 36. Nut 74 is affixed to bar 72 with the nut openingcoaxial with collar 36 and the single passageway through center board16. Damper 42 is supported, as in the previously described construction,upon a hollow tube. In this construction the damper support tube isthreaded from the upper instead of the lower end, and therefore denotedby reference numeral 76, although in other respects being the same astube 46.

The lower end of tube 76 extends into the passageway through centerboard 16. A pair of slots, one of which is seen in FIG. 6 and denoted byreference numeral 78, extend from the lower terminal end of tube 76, onopposite sides thereof.

An adjustment tool, denoted generally by reference numeral 80, includesshank portion 82 having a pair of strips 84 extending from one endthereof with ears 86 bent inwardly from each. Molded bushing 88 isplaced on the opposite end of shank 82, fitting tightly thereon, and cap90 is secured to the shank end with a suitable adhesive or other means.Central opening 92 is formed in the end wall of cap 90. Shank 82 is ofsubstantially the same diameter as damper support tube 76, and may thusbe inserted into the passageway through center board 16 from thedownstream side of module 10 for engagement of ears 86 with slots 78.Rotation of tool 80 is transmitted to tube 76, whereby the latter ismoved axially due to its threaded engagement with nut 74 and theposition of damper 42 is changed with respect to the air inlet openinginto plenum 40 to adjust the rate of air flow.

Pressure measurements may be taken by inserting a pitot tube throughhollow damper support tube 76 to obtain direct readings of the rate ofair flow through the air inlet opening in collar 36 into filter plenum40. Since adjustment tool 80 is in axial alignment with tube 76 whenengaged therewith, the pitot tube may be extended through both and therate of air flow adjusted simultaneously with taking the readings. Pitottube 94 is first inserted through opening 92 in end cap 90 and advancedto extend through tool 80. After the sealing plug is removed from thelower end of the opening in center board 16, tool 80 is inserted andears 84 are engaged in slots 78. Pitot tube 94 is advanced throughdamper tube 76 to a position such as shown in FIG. 6, with its upper endextending above damper tube 76, into the area above damper 42 and collar36.

An opening is provided in terminal end 96 and a plurality of smallopenings 98 are provided through the wall of pitot tube 94 adjacent end96. The lower portion of pitot tube 94 remains outside the lower end oftool 80, lower end 100 and side port 102 being connected to the totaland static pressure taps, respectively, of pressure gage set 104. Thereadings of total and static pressure are converted by the gauge set inknown manner to a scale reading in cubic feet per minute of air flow inthe area just above damper 42. The flow rate may be adjusted by rotatingadjusting tool 80 while continuing to make air flow readings until thedesired flow rate is established. While the hollow adjusting tool andpitot tube with gauge set facilitates and expedites the measurement andadjustment of the rate of air flow into module 10, the hollow dampertube may be utilized without the special adjusting tool, taking flowreadings with a conventional velometer and rotating the damper tube witha screwdriver.

Although only leak testing is specifically shown and described inconnection with the first construction, and only air pressuremeasurement in connection with the second, it is obvious that eitherconstruction could, and preferably would, include features permittingboth leak testing and pressure measurement, as well as damperadjustment, to be performed from the downstream side of the filtermodule with only a singly passageway through the center board. In theconstruction of FIGS. 1-4, for example, the lower end of damper supporttube 46 would be slotted for engagement by an adjusting tool to rotatethe tube within the threaded fitting 52 to effect adjustment of theposition of damper 42. Preferably, the adjusting tool would also be inthe form of a hollow tube, such as that of FIGS. 7 and 8, whereby airpressure and flow rate measurements could be made in the mannerdescribed in connection with the second construction.

Likewise, leak testing could be performed entirely from the downstreamside of the filter module of FIG. 6 by injecting test smoke through awand inserted into the passageway through centerboard 16 to extendthrough hollow damper tube 76 to the area above damper 42. Theconcentration of test smoke on the upstream side of the media could bemonitored in the manner of the construction of FIGS. 1-4 by providingcommunication as illustrated therein between enclosed space 40 and thedownstream side of the passageway through centerboard 16. That is, anadditional hollow tube, surrounding the lower end of damper support tube76 and sealed thereto, having apertures within plenum 40, would beprovided and utilized with the system shown in FIG. 6. In any case, thedamper is supported upon a hollow tube mounted for adjustable, axialmovement with access via a single passageway through the centerboard ofthe media core, whether supported in a threaded coupling at the upper orthe lower end.

What is claimed is:
 1. In a down-flow, HEPA-type air filter apparatushaving a core of pleated filter media separated into two halves by alaterally extending center board, said media being sealingly engagedwith said center board and with a box-like enclosure having a top wallabove said core to define an enclosed space on the upstream side of saidmedia, said top wall having a centrally-disposed, circular opening foradmitting air from ductwork connected thereto into said enclosed spacefor passage through said media, the combination comprising:(a) a dampermounted for adjustable vertical movement with respect to said top wallto control air flow through said opening; (b) at least one passagewayextending through said center board between the upstream and downstreamsides of said media co-axially with said damper and top wall opening;(c) a first hollow tube fixedly attached to said center board andextending from a lower end within said passageway to an upper end withinsaid enclosed space; (d) an internally threaded nut fixedly mounted uponthe upper end of said first tube; and (e) a second hollow, elongated,tube coaxially aligned with said passageway and having a lower endthreadedly engaged with said nut, said damper being supported upon saidsecond tube adjacent the upper end thereof, whereby the position of saiddamper relative to said top wall opening may be adjusted by threadedmovement of said second tube through said nut, and whereby a probe maybe inserted through said passageway in the center board and said secondtube from below said filter to above said damper.
 2. In the apparatusaccording to claim 1 wherein said damper is conical and has a lowerdiameter at least as great as said top wall opening.
 3. In the apparatusaccording to claim 2 and further including a generally cylindricalcollar member extending upwardly from said top wall opening.
 4. In theapparatus according to claim 3 wherein said collar includes a lowerportion tapering outwardly to a circular flange.
 5. In the apparatusaccording to claim 4 wherein said flange is positioned within saidenclosed space and said collar, inwardly of said flange, extends throughsaid top wall opening.
 6. In the apparatus according to claim 1 whereinthe inner diameter of said first tube is larger than the outer diameterof said second tube, whereby an annular space is provided between theportion of said second tube lower end extending through said nut and theinner wall of said first tube.
 7. In the apparatus according to claim 6wherein at least one opening is provided through the wall of said firsttube within said enclosed space, for communication of said enclosedspace with said annular space.
 8. In a down-flow, HEPA-type air filterhaving a core of pleated media separated into two halves by a laterallyextending center board, said media being sealingly engaged with saidcenter board and with a box-like enclosure having a top wall above saidcore to define an enclosed space on the upstream side of said media,said top wall having a centrally-disposed, circular opening foradmitting air from ductwork connected thereto into said enclosed spacefor passage through said media, the combination comprising:(a) a dampermounted for adjustable movement with respect to said top wall to controlair flow through said opening; (b) at least one passageway extendingthrough said center board between the upstream and downstream sides ofsaid media co-axially with said damper and top wall opening; and (c) ahollow, elongated, damper mounting tube coaxially aligned with saidpassageway, said damper being supported upon said tube intermediate oflower and upper ends thereof; (d) said lower end of said damper mountingtube extending into said passageway for sliding movement therein, andsaid upper end of said damper mounting tube having external threads; (e)a generally cylindrical collar member extending upwardly from said topwall opening; (f) a nut, fixedly supported upon said collar coaxiallytherewith, through which said damper mounting tube upper end threadedlyextends for adjusting movement of said damper with respect to said topwall opening and whereby a probe may be inserted through said dampermounting tube from below said filter to above said damper.
 9. In theapparatus according to claim 8 wherein said damper mounting tube lowerend includes engagement means for a tool inserted into said passagewaywhereby said damper mounting tube may be rotated to effect adjustingmovement of said damper from a position on the downstream side of saidfilter.
 10. In the apparatus according to claim 9 wherein saidengagement means comprises a pair of slots extending from the terminallower end into the wall of said damper mounting tube.
 11. In theapparatus according to claim 10 and further including a tool comprisinga hollow, tubular body having an external diameter of said dampermounting tube and an end portion adapted for engagement with said pairof slots, whereby said tool may be inserted in said passageway from thedownstream side of said filter and manually rotated to impart rotationto said damper mounting tube and adjusting movement to said damper. 12.A method of leak testing downflow, HEPA-type air filters having a coreof pleated filter media separated into two halves by a laterallyextending center board and with a box-like enclosure having a top wallabove said core to define an enclosed space on the upstream side of saidmedia, said top wall having a centrally disposed opening for admittingair from ductwork connected thereto into said enclosed space for passagethrough the media, said method comprising:(a) supporting a damper foradjustable vertical movement with respect to said opening by means of ahollow damper support tube extending coaxially through said opening; (b)providing a passageway through said center board coaxially with saiddamper support tube; (c) inserting the hollow wand of a test smokegenerator through said passageway and said damper support tube toposition the outlet end of said wand above said damper, outside saidenclosed space; (d) injecting test smoke through said wand to be carriedby air flow from said ductwork through said opening and over said damperinto said enclosed space; and (e) scanning the downstream face of saidfilter core with a detector responsive to the presence of said testsmoke at said downstream face.
 13. The method according to claim 12 andcomprising the further step of monitoring the concentration of said testsmoke within said enclosed space while injecting said test smoke throughsaid wand.
 14. The method according to claim 13 wherein said monitoringstep is carried out prior to said scanning step.
 15. The methodaccording to claim 14 wherein said monitoring step is performed byproviding communication between said enclosed space and said detectorthrough the annular space surrounding said wand within said passageway.